SEX CONDITIONS 



proximate equality to such decided inequality 

 that tissues of either type may represent but a 

 minute portion of the specimen. Furthermore, 

 the region on either side of this plane may con- 

 tain tissues of the opposite genetic constitu- 

 tion indicating more or less wandering of nuclei 

 in the embryonic syncytium. Occasionally lack 

 of segregation may be so extreme that the re- 

 sulting mosaic is an irregular patchwork. Read- 

 justments during later embryonic development 

 may, moreover, cause intermingling of adjacent 

 tissues differing genetically. 



In certain normal wasps , there occur two non- 

 allelic, recessive genes both of which cause the 

 eyes to be whitened. For convenience, these 

 genes are called white and ivory. One interest- 

 ing combination of these colors occurs in the 

 mosaic compound eye, one section of the eye be- 

 ing genetically white, the other genetically 

 ivory. Such an eye might be expected to look 

 uniformly white; however, such is not the case. 

 The white, non-ivory region remains white and isi 

 sharply marked off from the ivory, non-white 

 region by a black border which grades impercep- 

 tibly into the ivory (Fig. 13) (A. R. Whiting, 

 1933b). The double dominant character is recon- 

 stituted in the region where the two recessives 

 are in contact even though there is no diploid 

 tissue present there. This phenomenon is thought 

 to be the result of the diffusion of some sub- 

 stance from the white region into the ivory. 

 Another instance of the effect of one gene upon 

 another is exhibited in the progeny of a female 

 heterozygous for ivory and cantaloup eye colors. 

 Such a female set as a virgin may produce, in 

 adiition to the four genotypes of sons regular- 



85 



